There are many different types of memory, including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), flash memory, resistance variable memory, such as phase change random access memory (PCRAM) and resistive random access memory (RRAM), and magnetic random access memory (MRAM), such as spin transfer torque random access memory (STT RAM), among others.
MRAM devices can employ a storage material that can be viewed as a multi-state resistor due to different relative orientations e.g., parallel and antiparallel, of the magnetic moments, which can change the magnitude of a current passing through the device. The storage material can transition the between different relative orientations. For example, in a write process, currents passing through conductive lines. e.g., word and/or bit lines, can be used to switch a magnetic orientation of the storage material, which can place the device in a high or low resistance state. A read process can then be used to determine the state of cell. For the STT memory cells, spin transfer torque, which can also be referred to as spin transfer switching, can be utilized to switch a magnetic orientation of the storage material, thus changing a resistance of the STT memory cell.
STT utilizes spin-polarized current, e.g., a current where most of the electrons have spins aligned in the same direction, which is applied to the storage material. The electrons may get repolarized due to the orientation of the magnetic moments of the storage layer. This repolarizing of the electrons can lead to the storage material experiencing a torque associated with the change in the angular momentum of the electrons as they are repolarized. As a result, if the current density is high enough, this torque has enough energy to switch the orientation, e.g., the direction, of the magnetization of the storage material. The advantages of using STT memory cells can include a smaller footprint, reduced space requirements, less number of steps in writing as compared with other writing techniques, scalability for large arrays, and/or lower writing current requirement, among others, as compared to some other memory cells.